M4 Sherman: Firepower

An earlier attempt was made to fit a 17 Pounder weapon system in a native Cromwell chassis. These later saw action, but the Sherman proved a more convenient platform at the time.

There was a program to develop a tank based on the A27M Cromwell chassis that would take the gun. The tank would have been known as the “Challenger.” However, it was experiencing problems and delays. No provision was made for deep wading (which would be important if it was to take part in the upcoming invasion of Normandy) and the design was high-sided and vulnerable. With D-Day approaching, and the need for a tank armed with the Q.F. 17 Pounder being years overdue, the British needed a solution and they needed it badly.

The Firefly would be the brainchild of W.G.K Kilbourn who was working for the Department of Tank Design. Being a project that was practically parallel to American attempts to up gun the Sherman, the British would run into similar problems; the biggest being the turret. Unlike the U.S., England had no access to new turrets to swap in place of the old turret. Because of this they would simply have to tolerate having a cramped turret. But the problem wasn’t that simple: The 17 Pounder recoiled a full forty inches when fired, and that would cause it to smash against the back of the Sherman turret and possibly knock the gun out of battery, or damage the piece itself not to mention the radio which was located at the rear of the turret.

Legend has it that the gun was turned ninety degrees to fit into the turret. Well, it was – and this helped to facilitate left-handed loading. But the problem was much, much more complex than that. The recoil system had to be completely revamped. The cradle for the gun tube had to be modified to fit, and that caused problems in itself because the piece was no longer properly supported. To fix this, the chase (the material that tapers from the breech to the barrel) had to be lengthened through a painstaking manufacturing process. The turret bustle housing the radio had to be extended to make more room. In addition ammunition for the 17 Pounder was much larger than the ammunition for the 75-mm M3, which means that ammunition storage needed to be rearranged, as did crew accommodations! The turret had to have a new hatch added to facilitate quick escape for the crew due to the bulk of the gun. The bow gun and its gunner, who was also the assistant driver, were wholly deleted to add more space for ammunition.